The enzymatic synthesis of esters from fatty alcohols and fatty acids is known. Enzymatic synthesis is an environmentally friendly process, in which the synthesis takes place with complete evaporation of the water of reaction formed.
The industrial use of lipases for preparing fatty acid esters has been described, for example, by Geoffrey Hills in Eur. J. Lipid Sci. Technol. 105, 2003, pp. 601-607. The fatty acid esters produced, particularly myristyl myristate, are produced in a fixed-bed process, in which the reactants are pumped several times through the column and the water of reaction formed is evaporated off under reduced pressure.
Fatty acid esters are used to an increasing degree in cosmetic skin care products as oil bodies or emollients. In order to meet the high demands of the market with respect to sensory properties and optimal dermatological tolerance, novel oil bodies and oil body mixtures are continuously being developed and tested. Innovative technologies for preparing these fatty acid esters are also part of this.
The synthesis of esters from fatty alcohols and fatty acids, as previously stated, forms water which must be removed in order to shift the reaction equilibrium towards a complete synthesis. The enzymatically catalysed preparation of fatty acid esters must be performed at relatively low temperatures, in order to maintain the optimal enzyme stability. Accordingly, a very strong vacuum is required to evaporate the water. This evaporation is very energy-intensive.
It has additionally been shown that problems arise when scaling-up to batch reactors. In typical production reactors of 10-100 m3, the water evaporation occurs, by means of the pressure drop, only in the upper layers due to the fill depth. It has further been found that the reaction is very rapid up to a conversion of 80-90% and typically proceeds in less than five hours. However, the result of this is that the amount of water formed in a production reactor during this period cannot be removed by industrial means, or can be removed only with very large equipment resources. Furthermore, the required energy input, which is necessary for the evaporation of the water of reaction, can be introduced into the reactor only with difficulty owing to the low internal temperature in the reactor.
A further problem lies in the fact that the enzyme catalyst has only very low stability at high temperatures or becomes inactive. It is known that enzymes are very temperature-sensitive. Thus, the ester synthesis cannot take place at temperatures greater than 60-80° C. It has particularly been found that the long-term stability of the enzymes falls in the presence of short-chain alcohols and short-chain fatty acids (C8/C10) at even lower temperatures, from about 40° C., such that the reaction should ideally be carried out at temperatures around 40° C.